services/binary-cache: cherry-pick nar-serve patch

Signed-off-by: Florian Klink <flokli@flokli.de>

services/binary-cache/default.nix

@@ -1,10 +1,30 @@
 # SPDX-FileCopyrightText: 2022-2024 TII (SSRC) and the Ghaf contributors
 # SPDX-License-Identifier: Apache-2.0
-{config, ...}: {
+{
+  config,
+  pkgs,
+  ...
+}: {
   services = {
     harmonia = {
       enable = true;
       signKeyPath = config.sops.secrets.cache-sig-key.path;
+      package = pkgs.harmonia.overrideAttrs (old: {
+        patches =
+          old.patches
+          or []
+          ++ [
+            # Cherry-pick of https://github.com/nix-community/harmonia/pull/293 into 0.7.3
+            # We can't bump to 0.7.5 in release-23.11 as it brings a libnixstore bump
+            # with backwards-incompatible changes (for a new Nix version).
+            # Sent upstream in https://github.com/NixOS/nixpkgs/pull/297989,
+            # can be dropped here once nixpkgs channel moves past that.
+            (pkgs.fetchpatch {
+              url = "https://github.com/nix-community/harmonia/pull/293/commits/3232511db91b7dce97172a8b018f0056585890f5.patch";
+              hash = "sha256-BQ2eJkPTKnwa62dqy6qe7Jq+wJ2Ds5VhT5ST/xVlHiQ=";
+            })
+          ];
+      });
     };
   };
   networking.firewall.allowedTCPPorts = [5000];